Lead acid and calcium batteries have been in use in industrial plants for more than a hundred years. Such batteries are usually arranged in banks of individual cells of 2 VDC (volts direct current), and such banks of batteries typically power direct current emergency buses which are normally rated between 48 VDC and 250 VDC. Industrial batteries are simple, chemical reaction devices, but their operating characteristics are relatively complex and vary considerably because they are dependent upon battery construction, manufacturing material and processes, ambient temperatures, aging, use and other factors.
A relative newcomer to the battery industry is the valve regulated lead acid (VRLA) battery technology utilized extensively in 48 VDC applications within the communications industry. VRLA batteries are used because they are smaller, lighter and require less maintenance than conventional flooded lead acid cells. However, VRLA batteries are less durable and are more sensitive to high temperature conditions and improper charging, and this has led to premature failures of the VRLA batteries in many applications.
As a result of the foregoing considerations, periodic surveillance testing methods have been utilized to ensure that battery cells and banks are and remain in a condition of operational readiness. Such testing methods are dependent on periodic measurement of the float charge at the battery terminals, charger output current and voltage, electrolyte levels, cell temperatures, pilot cell voltage and specific gravity, and such testing is also dependent on periodic discharge testing of the battery bank. However, this type of surveillance has several inherent problems: it is very labor intensive, and thus very expensive to perform; its accuracy is not always dependable since it relies on inaccurate instruments and techniques which do not always compensate for such parameters as temperature, aging, environmental factors, and specific charge-discharge characteristics; load testing usually requires disconnection of the emergency battery bank from its critical load and also on drawing the battery state of charge to very low levels; load testing of the battery bank is the only way to ensure battery performance and is the best way to detect cable continuity and degradation of material because of oxidation or other chemical deterioration, and thus the reliability of the system is virtually unknown between tests; trend analysis of cell operational parameters is not performed during load testing (for example, when temperatures are abnormally increasing, internal cell faults may go unnoticed); there is no accurate indicator to predict that, after a full load testing, each battery cell will perform the same as before the test; and emergency stand-by or uninterruptible power supply (UPS) batteries, which are continuously on a floating charge and are not often exercised, tend to deteriorate faster than working batteries and to require "stabilizing charges" more often, and both of these conditions increase operational and maintenance costs.
In evaluating systems of the prior art, it is important to note that the measurement of cell conductance or open-circuit voltage does not provide a good indication of battery capacity or ability to carry a load for a predetermined time. A half-discharged battery may show a voltage near to its fill charge after a period of rest, and any correlation between cell conductance and capacity is speculative.
Finally, there have been two ways in the prior art to calculate accurately the state of charge: the "rate dependent capacity" method and the "model based" method. Both of these methods require the measurement of operational parameters, such as voltage, specific gravity of the electrolyte, temperature, transient discharges, battery specific characteristics, and other parameters. Moreover, both of these methods are labor intensive, and require local battery surveillance and maintenance.
Therefore, there is a need in the prior art for an on-line battery monitoring system which ensures readiness and reliability of UPS and emergency battery systems, while eliminating labor intensive surveillance testing, extending the life of the cells, and allowing for remote monitoring and testing of emergency battery systems. There is also a need in the prior art for such an on-line battery monitoring system which performs these services with high accuracy and reliability while never removing the batteries from their normal service.
There is also a need in the prior art for the development of an on-line battery monitoring system which performs non-intrusive testing, accurately and remotely monitors the condition and operability of industrial UPS and emergency battery systems, and automatically determines the following conditions for individual cells and battery banks: state of charge, capacity, location and magnitude of grounds, location and magnitude of connection degradation, and internal cell faults and degrading conditions.
The following U.S. pat. Nos. are considered to be representative of the prior art relative to the invention disclosed herein: 4,707,795; 4,888,716; 5,027,294; 5,047,961; 5,193,067; 5,268,845; 5,287,286; 5,295,078; 5,311,441; 5,321,626; 5,349,535; and 5,450,007. However, none of the patents cited above provides the capabilities or functions provided by the system of the present invention. For example, the systems previously disclosed do not perform some or all of the following functions: battery bank capacity testing, battery cell capacity testing, accurate calculation of individual cell SOC, non-intrusive cell electrolyte level indication, leakage resistance testing to earth ground, and customized battery monitoring. Other features not disclosed in the prior art will become evident from the detailed disclosure set forth below.